Site Amplification in the Los Angeles Basin from Three-Dimensional Modeling of Ground Motion

Abstract It is well established that sedimentary basins can significantly amplify earthquake ground motion. However, the amplification at any given site can vary with earthquake location. To account for basin response in probabilistic seismic hazard analysis, therefore, we need to know the average amplification and intrinsic variability (standard deviation) at each site, given all earthquakes of concern in the region. Due to a dearth of empirical ground-motion observations, theoretical simu-lations constitute our best hope of addressing this issue. Here, 0–0.5 Hz finite-difference, finite-fault simulations are used to estimate the three-dimensional (3D) response of the Los Angeles basin to nine different earthquake scenarios. Amplifi-cation is quantified as the peak velocity obtained from the 3D simulation divided by that predicted using a regional one-dimensional (1D) crustal model. Average ampli-fication factors are up to a factor of 4, with the values from individual scenarios typically differing by as much as a factor of 2.5. The average amplification correlates with basin depth, with values near unity at sites above sediments with thickness less than 2 km, and up to factors near 6 above the deepest (! 9 km) and steepest-dipping